[lworld] RFR: 8359370: [lworld] allow instance fields of identity classes to be readable in the prologue phase [v15]

[Vicente Romero]

On Fri, 29 Aug 2025 10:47:27 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Vicente Romero has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   removing unnecessary imports
>
> src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java line 1449:
> 
>> 1447:                              * not allowed in the prologue
>> 1448:                              */
>> 1449:                             if (insideLambdaOrClassDef ||
> 
> I'm not entirely convinced about these checks. They seem to lead to very strange asymmetries:
> 
> 
> import java.util.function.*;
> 
> class Test3 {
> 
>     int x = 4;
>     int y;
> 
>     Test3() {
>         System.out.println(x); //error
>         Supplier<Integer> s1 = () -> x; // error
>         y = 2;
>         System.out.println(y); // ok
>         Supplier<Integer> s2 = () -> y; // error
>         super();
>     }
> }
> 
> 
> I understand that references to `x` are invalid here -- `x` is not a strict field, so it will be initialized _after_ the prologue. So the first couple of references are errors, fine.
> 
> But in the last couple, we have that `print(x)` is good, but the reference from the lambda is flagged as an error. I'm not sure what's the rationale here? After all the lambda is defined _after_ `y` has been assigned, so what are we trying to protect against?

I think that the idea of restricting the access from lambdas and local classes is that they will capture `this` in order to access the field(s)

> src/jdk.compiler/share/classes/com/sun/tools/javac/tree/TreeInfo.java line 1010:
> 
>> 1008:                 return node.type.tsym;
>> 1009:             return null;
>> 1010:         case TYPECAST:
> 
> Is this still needed?

yes no for this patch, but I was wondering if it could be useful for future use. But I will remove it

-------------

PR Review Comment: https://git.openjdk.org/valhalla/pull/1523#discussion_r2309862398
PR Review Comment: https://git.openjdk.org/valhalla/pull/1523#discussion_r2309865193